Anomaly Scan (20 weeks)

This transbdominal scan can detect about 70% of major structural abnormalities, a low lying placenta (placenta praevia) and rarely a blood vessel which overlies the placenta (vasa praevia) which can cause lethal bleeding in labour. In the UK the RCOG have identified specific views and structures which should be checked at NHS Anomaly Scans but screening for vasa praevia is not included. Some support groups feel this should be universally offered.

This is a detailed scan during which each part of the fetal body is examined. Special attention is paid to the brain, face, spine, heart, stomach, bowel, kidneys and limbs. If any abnormalities are detected the significance of the findings will be discussed and the couple will be given the opportunity to have further counselling.

The purpose of Anomaly scans is to check development of the baby and it is normally performed at around 20 weeks. Most babies are healthy but sadly some have serious problems, which cannot always be predicted by a family history or the health of the mother. When you attend for this scan we will assume that you wish to know about all problems that are detected by the scan and any concerns that are raised. The scan is performed by a specialist sonographer or doctor. The scan is performed through the tummy wall but occasionally we may need to perform the scan through the vagina if the baby’s head is low in your tummy in order to check the developing brain.

We have a full counselling service either over phone or face to face in our clinic should any problems be detected and we will send a copy of our report to your referring hospital, doctor or midwife to ensure good communication between all parties. This is because if we make recommendations on the scan such as a low placenta, this will need a repeat scan again later in the pregnancy to check that it has moved out away from the neck of the womb.

We routinely assess:

Head Circumference (HC)

Femur Length (FL)

Amniotic Fluid

Placental location

Viability (heartbeat)

Most major abnormalities may also be seen

Gender (sex of baby) is optional

Detection Rate of Common Anomalies at the 20 Week Anomaly Scan

Problem

What we see

Detection

Spina bifida

Open spinal cord

90%

Anencephaly

Missing top of head

99%

Hydrocephalus

Excess fluid within the brain

60%

Congenital heart disease

Major heart defect

60%

Exomphalos / gastroschisis

Defect of the abdominal wall

90%

Major kidney problems

Missing or abnormal kidneys

85%

Major limb abnormalities

Shortened or abnormally formed bones

90%

Diaphragmatic Hernia

Defect of the muscle separating chest and abdomen

65%

Cleft lip and palate

80%

Down’s Syndrome

May be associated with heart, limb, and bowel problems

50%

Cerebral palsy

Severe learning difficulties

Not seen

Autism

Not seen

Detection Rate of Common Anomalies at the 20 Week Anomaly Scan

Most Anomaly scans are carried out transabdominally (through the tummy) with an abdominal probe and a full bladder is helpful.

The Anomaly Scan will identify about 99% of babies with conditions like spina bifida, about 50% of babies with major heart defects but only a few babies with bone growth problems (skeletal dysplasias). It cannot detect cerebral palsy, autism and learning problems.

The ability to check the baby’s development is dependent upon many factors. The bodyweight of the mother and the manner in which the baby lies in the womb are major issues. However, sometimes we cannot obtain what we consider perfect views of a certain part of the baby’s body. In this case you will be invited back for a repeat scan. This happens in about 10% of cases so please do not be alarmed if this happens to you. You are only charged for the one visit no matter how many times we need to bring you back.

About 70%of all serious congenital malformations can be detected by the 20 week scan. Thus if the baby appears normal on scan there is only a small chance that your baby will have a problem. This is because some problems may not be present at 20 weeks but develop later in the pregnancy e.g. diaphragmatic hernias where there is a small hole in the muscle between the lungs and the bowels.

As well as being scanned by one of our expert sonographers, all our patients will have access to Dr Bryan Beattie, Consultant in Fetal Medicine, for further advice should any problems arise.

We will also give you some black and white photographs of your scan.

We check the development of the following organs or movements on the anatomy scan: head, brain, face, spine, arms, hands, fingers, heart, lungs, bowels, kidneys, bladder, legs, feet, the fluid around the baby, the umbilical cord and position of the placenta.

We have included a table of some of the problems that can be detected on ultrasound at 20 weeks and the likelihood of detection. (in part ref ; RCOG 20)

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